If 15% of claim value (which is highly subjective anyway) really...

If 15% of claim value (which is highly subjective anyway) really is an appropriate valuation basis, IMF wouldn’t be moving to a funds management model !

For example there are plenty of enormous international arbitration claims out there where any funder would bite your hand of to get a 15% return. First you have to win the case, then you have to get an acceptable damages outcome, then you have to survive an appeal, and finally you have to enforce. All of that could take 6+ years.