The RealTracks will work with 2015.

What everybody else is referring to is the styles. There is a change in the picture and your 2015 StylePicker has difficulties to address the 2016 styles. But the RealTracks are not affected.

It is just bad luck on your side that some major changes are done while you're entering the (moving) train.

You said that updating is expensive. Since I don't know you and your circumstances I cannot argue. I only can state some facts. The current price for the update is USD 129. The last years the update price during the discount season was USD 99 (if you had the current version of that time).

You don't have to buy the complete version, the update, called the PlusPAK, is sufficient. This PlusPAK also includes all the regular styles and RealTracks that are new with BIAB 2016.

Having said this, there is a 49-PAK with some more RealTracks which is available in August 2016, because of the new Xtra styles that reference some of these RealTracks. These may or may not be included in the 2017 version.

Desktop; i7-2600k, 8 GB mem., Win 10 Pro, BIAB 2017; RB 2017 - latest build
Laptop: i5-2410M, 4 GB mem, Win 10 Pro, BIAB 2017; RB 2017 - latest build