Hello there.
With this guide I'll help in how you solve the issue of lag in TS 64 edition.

First check if you have frame rate issues on the 32 bit edition just in case. if you have none then continue with this guide.
If you do have terrible frames no mater what version you play, Then this guide will not help you.
If you have frame rate issues on the 64 bit (Including DX12 experimental version) only then this should help you.

But first: Reason for the lag. It turns out that this issue occurs with people for for example have multiple graphics cards.
( Example: Laptop )
The default for Nvidia is 32 bit to run on. But it does support 64 bit, We only have to add TS 64 editon to its settings.
Same for the Experimental one if you want.

- Open your nvidia control panel.
Variant A: Right click
Variant B :Right click, Show more options
And select ''Nvidia control panel''

- Click ''Manage 3D Settings'''

- Then click ''Program Settings'' and find railworks64.exe file and add it to the program settings.
Same for the Experimental one if you want.
Make sure to select the Nvidia processor

https://steamuserimages-a.akamaihd.net/ugc/2478761126838537831/7723312B50BC89F28E8C94CB2CCEDBAF50DB4596/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

Hope this help