I'd say a lima shovelnose in a 150 is a bad idea long term. Vulture cats also get too large. For relatively sedentary cats (e.g. bullhead, Chaca chaca, Doradids, etc.) you could probably go with anything up to a 16-18" maximum size, but for more active species (e.g. synodontis, most pimelodids, and just about any non-bottom dwelling species), I'd say stick with sub-14" fish.
The larger (12-14") Synodontis species would do well for you, but Synos aren't fast growers, so you'd probably have to find them at adult size. Other options include bullheads (10-14"), several Pseudopimelodids (10-16"), the larger Pimelodus species like P. ornatus (mostly 9-12"), Ageneiosus marmoratus (12"), and a few of the smaller Chrysichthys species (C. brevibarbis, graueri, and auratus which range from 14-16").