I think that I have one WSW product, but I have hundreds of 1/87 vehicles from Roco, Trident, Arsenal-M, CMK and more so I have contemplated which figures go best.
I generally feel that 15mm figures work far better with 1/87 – especially when the figures are based a la Flames of War. It isn't perfect, the figures are clearly smaller than comparable 1/87 figs. But, if all you're using is 15mms, then they "look right."
To demonstrate, this picture is a group of Battlefront US riflemen with two Roco RSO tractors picture
Compare to the same vehicles with 1/87-scale Preiser figures picture
What I did find, while testing out 15mm figures, is that Resistant Roosters' German figures are closer to 18mm in height and therefore really work well with this scale. I also found that Peter Pig's driver and passenger figures fit better inside a 1/87 scale vehicle than many Roco or Preiser figures.
Wyatt