Globular clusters more or less all look the same. And this is true of M15 and M2. M15 is billed as one of the densest globular clusters and it does photograph well. (I still think M13 in Hurcules is the best).
M15 and M2 are described as being 18′ and 16′ in diameter (angular size when viewed from earth). M15 is listed as mag 6.2 while M2 is mag 6.3 – hardly a discernible difference. However, photographically M15 came out much better. This is mostly due to M2 being quite low on the horizon from my lat 45° site.
I first to 2hrs of images of M15.
Then i turned the scope to M2 and took another 2hrs of data. M2 was only 9° above the horizon when i finished. I may have lost focus as well as the temp change was significant.