Depends on the fine print of the deal (if it exists at all) and your immediate needs.
If this deal prevents a future upgrade subsidy, you may want to futureproof yourself with something a little more modern like the 8/X/XR/XS.
If there are no strings attached and this has no impact on future purchases or promotions in the next 12-24 months, then this will certainly address your immediate hardware need. But I wouldn’t look at it as much of an upgrade.
keep in mind you will lose some features such as storage memory and your headphone jack by going from 6 to 7.
7 is getting on up there in age. But it will make calls, text, and run most iOS stuff that you know and love. I myself ran a 6S for 5.5 years (and would have had gone longer) if it didn’t develop hardware issues. But the semi-subsidized (bill credits technically) carrier programs we have here made signing onto a 24 month commitment result in an incremental increase of my monthly bill like $6 more after all of the other discounts etc, so I skipped right past options to fix my 6S, similar free or near free iPhone 7/8 options, dirt cheap SE2020 options, XS deals, 11 deals, and went right for a 12 pro. YMMV of course. But a “free” 7 would have got me back on my feet as well if I couldn’t justify the other options. But would recommended checking if you have options for 8 or above that you can rationalize value with.