15XX system tanks have advantages and disadvantages compared to 25XX tanks.
the 250XX tanks uses less chemistry for smaller quantities of film per process, but get less efficient as you stack them up. the 1500 are better when loaded full or with extensions, but they do not allow for 4X5 reels...
also - i have found that even with a flat level processor the 1500 tanks as they are smaller are more prone to uneven developing on one end of the drum (usually the bottom end), where less active developer ends up due to the design of the tank, 2500 tanks suffer less from this issue.
there is also something to be said about convenience difference in loading 1501 reels vs 2502. matter of preference really. after you get used to it they are pretty much the same.
2509 reels give really amazing results, and after comparing them with 3010 drum results i am not sure it is worth the huge extra cost, however, 3010 drums use much much much less chemistry (about 50% less for same amount of film when fully loaded), which might be worth while calculating in to the total cost of purchasing and operating a drum. also of course - 3010 drums are ONLY for sheet film, where as with your multi tank 5 you can mix and match 1X2509 and 2X2502 reels at the same time, basically trying to say, its more flexible.

any other questions..? ask away!