It depends on the weight of the deck. I have a 1210 that handles a 5' Caroni very well. It didn't have what it takes to use a (heavier) 5' Landpride. With the Landpride on the back, the 1210's front wheels lifted even with two small suitcase weights, and it struggled when cutting uphill.
Your 1510 has 6 more horses at the PTO than my tractor, so I wouldn't be afraid of a lighter weight 6-foot RFM.