It's been a long time since I used Schildbatch Wallet. Most of the time it was relatively quick to sync the wallet (a matter of minutes or a few hours).
It's fast if you let it sync regularly. Restoring a backup after years is an entirely different story

I don't remember if it downloaded "part of the blockchain" or block headers to verify transactions. In the case of Unstoppable, what exactly does it download? Part of the blocks (as if it were pruned), headers, etc? Is that why some are reporting it taking so long?
Let's test it: I'll restore the wallet I removed a year ago. I've selected all 4 Bitcoin address formats.
It's weird (and sneaky): it doesn't let me select "Blockchain" after I enter my seed phrase, it uses "Blockchair API" by default. So before I can change any settings, it has already shared my addresses with the API. So far for privacy, once it's shared, it's too late as my privacy is compromised already.
But after I changed it to "Blockchain", it started "syncing" from scratch. Currently:
Blocks Remaining - 641045
UpdatesMy phone (a high-end phone from 5 years ago) felt warm for hours.
I now have 4 different "BTC" thingies downloading: BIP86, BIP49, BIP86 and BIP44. The first one is 180,000 blocks ahead of the others, but the others aren't completely in sync either. There's up to 1000 blocks difference. Apparantely all address types have their own separate download.
After 3 hours, 15 minutes, BIP86 finished.
After about 6 hours, BIP86 finished. My phone is less warm already, and the sync seems to be slowing down.
After about 7 hours, BIP49 finished.
About 20 minutes later, BIP44 finished.
Unstoppable wallet downloaded 20.83 GB in total.