Definitely comes down to how you use your computer, and how much power you need. The great thing I find with Mac is that they are very capable for many years.
The things you want to consider before deciding to upgrade is, are you ok losing the ports? If you are considering a refurbished 2016 or 2017, those seem to be the most vulnerable to the keyboard issues, and stage lighting effect on the screen. 2016 and 2017 also still have the dual core where the 2018 and 2019 have the updated quad core, and the speed definitely shows.
Here's the good news, if you get the battery replaced regardless, right now your 2015 has the highest resale value you are going to see it having, and it would be a great time to sell it if you decide to upgrade. You could use that MacBook Pro to pay a good portion towards your new MacBook Pro. I think you would get that $200 battery replacement cost you pay up front on that back end of the sale and make it more marketable.
People have gotten very antsy with the new models, particularly with the keyboard issues with the butterfly design, so many are still purchasing the 2015's, and paying a premium for them. I am not reading any complaints yet on the 2019's and am thinking they may have finally found the true fix. The stage lighting also appears to be fixed.
Your money, and your call, but if you want new and rely on these for work and pleasure the way I do, you may serve yourself well going with the 2019, or a 2018 if you could get a really good deal.