You can load a 2502 reel a bit easier because the radius is larger. Especially when putting 2 120 roll films on one reel. Apart from that the 25xx system is designed for rotary development while the 15xx system normally is used for inverse processing. For the 15xx system in rotary you will have often a problem for the minimum amount of concentrate for each film in the small tank volume. Further the 25xx system you can use for 9x12cm or 4x5" sheet films.