DON’T!!!!!!!!!!!!
That’s to large a cut. Most people who reduce by 50% have awful withdrawals.
Keep in mind the length of time you’ve been taking this drug. Your brain isn’t likely to accept such a large cut.
Try cutting 30mg that’s a 10% cut. Although no one can predict an ideal percentage cut since there is such a big difference in how people react. One person had a horrible experience getting off Neurontin, I was on a larger dose and had no problems at all. If you look back you can read about all the people who regretted their decision of large cuts.
I understand it’s hard to go slowly but it’s really the only choice you have if you want to discontinue this medication safely with no withdrawals or at least the fewest possible withdrawals. Some have done it but it has taken along time.
Based on a 10% titration rate your looking at 3 years maybe slightly more.
If you don’t have any withdrawals during your fist months cut may you could try reducing every 3 weeks instead that might cut your time by 9 or so months.
A compounding pharmacy would probably be your best bet if that’s a feasible option.
Slow and steady is the best way to succeed
Good luck,
Jake

Hello--chiming in here...I assume you mean you've been on 300mg? DO NOT reduce to 150mg from 300mg. It will throw you into withdrawal, the likes of which I woudn't wish on anyone.
Read through all these posts.
Slow taper is how to best avoid the worst of WD symptoms. Slow taper=10-15% reduction in mg every month to month and half. Does it take awhile? yes, but it's worth avoiding the WD symptoms--trust us.

Why are you thinking about reducing? Is it causing you problems, or not working?