I have Friekorps 15 FPW figures. They are indeed true 15mm. I bought and painted them back in the early to mid-90s. I have several battalions of Prussians. I also have three battalions of Turcos, three of Zouaves, and one French Hussar regiment. I still use these but the bulk of my collection is Old Glory. The Old Glory figures are IMO the best range OG has.
The Friekorps 15's Zouave and Turcos are nicely done. However, I am not taken with their cavalry. The Prussians have both pickelhaube and field cap. The caps are a nice touch but the Pickelhaube is disappointing. The Friekorps 15's figures are very fragile. One drop on a hard floor and they tend to shatter. The OG figures are more durable. Overall I rate the OG range as superior.