Hi IRT and
to IIS, on those binoculars the 10x50 pair would be better as you can hold them in your hands and still get awesome views , but
the 15x70,s will show a lot more deep sky at the expense of portability, you could hand hold them but they will get heavy fast and every movement. , breath , twitch etc. will be magnified 15x and that gets old fast , yes you can lean against a wall , use a broom , lie down but they will still get heavy after a time.
Goodbye portability. , as you really need a tripod for big binoculars and then cost rears its ugly head and all of a sudden your $159 binoculars end up costing $250 plus , depending on type. , oh yes big binoculars are cool , I have some 80mm ones. Awesome but not very portable .
Others will chime in here for sure. , but in the end it is your call , I find I use my 8x56,s all the time. , hand held.
Brian.