Temporary Phone?

My Samsung Galaxy S6 refused today to power on. I'm taking it to a repair shop later this week. In the meantime, I've pulled out my old Galaxy S2. I want to use What's App on the old phone for a few days, but my Google Cloud backup for What's App is 18 months old! (Note to self, check these things more often.) I can't get to the database on the S6 as it won't power on at all.

So I'd like to use What's App on the old S2 for a few days without trying to restore the 18-month old database. Once the S6 is working again, how will I get this week's messages that arrived on the S2 back into the S6? Is that possible?

Or am I better off just not installing What's App on the S2 so that all this week's messages come in on the S6 as soon as it's repaired?

Thanks