K1.5V

Arguably, there is no good K1.5V standard. The Skiff MK compendium
shows that there are no stars with multiple independent K1.5V
classifications.  Gray06 classified 9 stars as K1.5V or variant,
the B-V colors for which show remarkably tight scatter.

Keenan99 standard: HD 13445 (HR 637) - K1.5V 

(B-V)(K1.5V) = 0.820 ; deprecated stan. HD 13445
(B-V)(K1.5V) = 0.859 ; N=9 Gray06 K1.5V stars (+-0.003 sem, +-0.009 rms)
(B-V)(K1.5V) = 0.887 ; exemplar HD 205390 = GJ 833 = HIP 106696
=> adopt (B-V)(K1.5V)   = 0.860 ; updated 2/22/2019
=> adopt (U-B)(K1.5V)   = 0.530
=> adopt (Bt-Vt)(K1.5V) = 1.000
=> adopt (V-Ic)(K1.5V)  = 0.910
=> adopt (V-Rc)(K1.5V)  = 0.476
=> adopt (R-Ic)(K1.5V)  = 0.434
=> adopt (V-J)(K1.5V)   = 1.560
=> adopt (V-H)(K1.5V)   = 1.973
=> adopt (V-Ks)(K1.5V)  = 2.069
=> adopt (H-Ks)(K1.5V)  = 0.096
=> adopt (J-H)(K1.5V)   = 0.413
=> adopt (Ks-W1)(K1.5V) = 0.030
=> adopt (V-Hp)(K1.5V)  = -0.144
=> adopt (W1-W2)(K1.5V) = -0.063
=> adopt (W1-W4)(K1.5V) = -0.016
=> adopt (G-J)(K1.5V)   = 1.341
=> adopt (G-Ks)(K1.5V)  = 1.850

(G-V)(K1.5V) =  -0.285 ; HD 13445 PM* K1.5V
(G-V)(K1.5V) = -0.265 ; interpolated between K1V-K2V 
(G-V)(K1.5V) = -0.255 ; HD 85390 PM* K1.5V
(G-V)(K1V)   = -0.253 ; smoothed fit f(SpT) G9V-M0V
(G-V)(K1.5V) = -0.250 ; trend SIMBAD d<20pc for V-Ks=2.069
(G-V)(K1.5V) =  -0.229 ; HD 119782 PM* K1.5Vk:
=> adopt (G-V)(K1.5V) = -0.255 [updated 9/21/2021]

(Bp-Rp)(K1.5V) = 1.0470  *_36_Oph_B  K1.5V(k)
(Bp-Rp)(K1.5V) = 1.050   fit for V-Ks=2.069
=> adopt (Bp-Rp)(K1.5V) = 1.05 [updated 7/17/2020]

(G-Rp)(K1V)   = 0.56   ; K1V mean
(G-Rp)(K1.5V) = 0.5820 ; *_36_Oph_B  K1.5V(k)
(G-Rp)(K1.5V) = 0.592  ; fit for V-Ks=2.069
(G-Rp)(K2V)   = 0.62   ; K2V mean
=> adopt (G-Rp)(K1.5V) = 0.59 [updated 7/17/2020]
=> adopt (Bp-G)(K1.5V) = 0.46 [updated 3/1/2019; Bp-Rp=1.05, G-Rp=0.59]

Teff(K1.5V) = 5038K ; non-stan. HD 205390/GJ833
Teff(K1.5V) = 5140K ; trend [Fe/H] vs. Teff (PASTEL compend.) for 25 Teffs/[Fe/H] pairs for Gray06 K1.5V stars (see below)
=> adopt Teff(K1.5V) = 5140K [updated 9/26/2019]

BCv(K1.5V) = -0.270 ; Casagrande08 calib for Teff=5140K, set so BCv(5772K)=-0.085
BCv(K1.5V) = -0.253 ; Flower96 calib for Teff=5140K, set so BCv(5772K)=-0.085
BCv(K1.5V) = -0.244 ; Masana06 calib for Teff=5140K, set so BCv(5772K)=-0.085
BCv(K1.5V) = -0.237 ; Bessell98 calib for Teff=5140K, set so BCv(5772K)=-0.085
BCv(K1.5V) = -0.230 ; Casagrande18 calib for Teff=5140K, set so BCv(5772K)=-0.085
BCv(K1.5V) = -0.209 ; Bertone04 calib for Teff=5140K, set so BCv(5772K)=-0.085
=> adopt BCv(K1.5V) = -0.24 [updated 9/26/2019, adjusted so that BCv(5772K)=-0.085]

Mv(K1.5V) =  5.94 ; trend for FGK d<25pc SIMBAD for B-V=0.86
Mv(K1.5V) = 5.95 ; Gray01/03/06 dwarfs, xHIP B-V/Mv, Gaspar16 |[Fe/H]|<0.05 "solar": fit for B-V=0.860
Mv(K1.5V) =  5.96 ; deprecated stan. HD 13445 
Mv(K1.5V) =  5.97 ; B-V=0.589, Wright04 calib
Mv(K1.5V) =  6.33 ; exemplar HD 205390/GJ833/HIP106696
=> adopt Mv(K1.5V)  = 5.95  [updated 9/26/2019]
=> adopt M_G(K1.5V) = 5.695 [updated 12/10/2020] (Mv=5.95, G-V=-0.255)

M_G(K1.5V) = 5.841 ; SIMBAD d<20pc trend for V-Ks=2.069

=> adopt M_Ks(K1.5V) = 3.884 [updated 9/26/2019; Mv=5.95, V-Ks=2.066, last updated 8/2/2018]

logL(K1.5V) = -0.388 ; Mv=5.95, BCv=-0.24, Mbol = 5.710
=> adopt logL(K1.5V) = -0.388 [updated 9/26/2019]
=> adopt Mbol(K1.5V) =  5.710 [updated 9/26/2019]

Rad(K1.5V) = 0.807 Rsun ; logL=-0.388, Teff=5140K
=> adopt Rad(K1.5V) = 0.807 Rsun [updated 9/26/2019]

# Deprecated Standard

HD 13445 = HR 637 = LHS 13
  K0V: Evans57
 *K1V: 1943HarCi.449....1H,Gray06,Houk78
  K1.5V: Keenan89,Keenan99

  Only Keenan considered this a K1.5V, with all other authors
  classifying it earlier.  White dwarf companion (GJ 82B) of type DQ6
  is ~2" away, probably contaminating the photometry. V=6.12(HIP),
  B-V=0.812+-0.015(HIP), B-V=0.820+-0.004(Mermilliod91),
  V-Ic=0.88+-0.02(HIP).  PASTEL compendium: <Teff> = 5190K(N=13),
  [Fe/H] ~ -0.2, logg ~ 4.6-4.7. Mv=5.96. 

# Exemplar

HD 205390 = GJ 833 = HIP 106696 
   K1V: Torres06
  *K1.5V: Gray06
   K2V: Evans57,Houk78

   All types in K1-K2 range. Not in WDS. V=7.136+-0.005(Mermilliod91),
   B-V=0.884+-0.005(Mermilliod91), B-V=0.887(Koen10), U-B=0.552+-0.207(Mermilliod91),
   J=5.518+-0.035(2MASS), H=5.137+-0.053(2MASS),
   Ks=4.970+-0.021(2MASS). PASTEL median Teff = 5038K(N=3),
   [Fe/H]=-0.17+-0.03(Valenti05), logg=4.62+-0.06(Valenti05).
   Mv=6.33+-0.02(Koen10).

HD 205390
   K1V: Torres06
  *K1.5V: Gray06
   K2V: Evans57,Houk78

HD 17925 = HR 857
   K0V: Joy47
   K1V: Popper42,Munch44,Houk88
   K1/2V: West72('mean of two')
  *K1.5V(k): Gray06
   K2V: Wilson62,
   K3: Bidelman85

# Other Stars

36 Oph B = HR 6401 = HD 155885
   G8V:: 1943HarCi.449....1H
   K0V: 1923LicOB..10..169L(K0),Abt84,Corbally84
  *K1Ve: Evans59, Bidelman85(K1)
   K1.5V(k): Gray06
   K2:III:: Houk82
   K3V: Adams35

   Not good agreement on type. Median is K1V. Mermilliod91 only
   provides unresolved/combined B-V=0.859+-0.007, V=4.323+-0.015,
   U-B=0.494+-0.017. Corbally84 provides resolved photometry:
   V=5.11, B-V=0.86, U-B=0.53. 

HD 177996 = GJ 4096 = HIP 94050 
  *K1V: Evans61(K1Ve),Houk78,Lu83,Torres06
   K1.5V(k): Gray06

HD 92945 = GJ 3615 = V419 Hya = HIP 52462
   K1V: Houk82,Torres06
  *K1.5V(k): Gray06

   Li-rich (EW(Li)=138mA;Torres06). V=7.75(Mermilliod91),
   B-V=0.89(Mermilliod91), U-B=0.56(Mermilliod91).

HD 6569 = UGP 16
   K1V: Houk88,Torres06
   K2V: Upgren72,McNeil86

   Evenly split, adopt K1.5V.

# Notes

Querying the 9 Gray06 K1.5V stars through PASTEL compendium, and fitting to the Teffs, I find:
Teff(K1.5V) = 5140K + 1.9003e2*[Fe/H]  ; rms = 63K