If you are looking at the 15X56 exclusively for tripod use and you are also looking at the Swarovski ATS65 spotter with the 20-50WA,
I'd go with the spotting scope. Like I said I have both and I purchased the 15X as carry binos (by no means back country carry).
If the primary use is long range glassing for hours go with the spotter.
If you need the flexibility of using a tripod or glassing without a tripod the 15X56 might be better.