Hello Alvaidas,
Because you are on the 2019 year end version for Dynamics GP 2015 R2, which is 14.00.1230, the ONLY supported upgrade path is to go to the equivalent 2019 year-end version of Dynamics GP 2016, which is 16.00.0814, then you can upgrade to the equivalent 2019 year-end version of Dynamics GP, which would be 18.2.1036 or later. Our latest release is 18.2.1060 as you mentioned.
The best way to remember the upgrade paths (along with using the hot topics), is that if you're currently on the mid-year or year-end release for GP version A, you must be upgrading to the equivalent or later mid-year or year-end release of GP version B.
There's been confusion recently, due to the moving to 18.2.xxxx and not using the same 16.0, 18.0 versions that we have been doing.
In the case of being on 14.00.1230, neither the hot topic to Upgrade to Dynamics GP 2018 nor Upgrade to Dynamics GP show this version as any valid upgrade path, so hopefully this helps answer your questions.
Please let me know if you have any questions.
Thank you,