I think you did have. If you can manage the 15x50's 1180 gram weight while walking (really needs to be ascertained before any final decisons), then that would be a clear upgrade over the 10x30's. At that weight level there would also be various non IS contenders with higher quality glass, from the lighter Bushnell 10x42 Legend M (750 grams) to the Nikon Monarch 5 16x56 (1230g). There's also the Steiner 2310 Nighthunter 8x56 (1090g) and currently on offer at £644.
I think you may have tbh. It's been said on these pages that the 10x30is (when stabilised) is roughly comparable to a budget 10x50 for stargazing, and the 12x36is a better quality 10x50. The 12x36 is definitely worth considering, but maybe not worth the extra expenditure or loss on selling the 10x30's.
I personally use a pair of Kowa 6x30 YF's while walking at night, as anything more substantial gets in the way of the exercising for me. I did try the 10x30is but made me feel nauseous, due to a perceptible slight swimming effect that affects a small percentage of users. 🙂