You also can't bring in Version 5.0 SpeedTrees used in TS10-TS12 due to a file format change made by the Speed Tree developer. Due to this issue, you need to replace your trees with something else that's compatible such as the CL Trees by Clam1952, or the RMM trees that will have updates available for them in T:ANE and up.
The best method to transfer your non-DLC/Payware routes is to clone the routes, if they're not yours. Update the trees, and then export the route to a CDP.
Import the route into TRS19. There will be faults, as in missing dependencies, and may a tree or two you missed. Download any dependencies that can be had from the DLS. This will find things that are on the DLS and also provide the latest fixed assets as well in some cases. Once the download is done, there's still stuff you'll need to retrieve from TS12 and such as any third-party assets, and dependencies of dependencies you may have missed. You can do this by opening up these assets for edit in TS12 Content Manager, and then importing the asset folder from the editing folder into TRS19 Content Manager. Depending upon the number, this process can take sometime, and sometimes it's faster to export them to a CDP. If you do open any assets in TS12, remember to commit them afterwards.
The thing is you may have to go back and forth a couple of times because there's going to be a tree or two that you missed in the replacement process, but once transferred over, your route will load up quite nicely. I've transferred in my routes from TS12 and older, and they are a world of difference better.
