Prosecutors are typically very skeptical about stories and testimonies in which information is left vague, where equivocations are rife, and where any witnesses other than the suspect's own partners are about as good as useless ---
Just when was the starting point for the 14 years?
Just where did Paul harass the early believers?
But hey, the Judean believers wouldn’t recognize me anyway.
The meeting with the Pillars was in private.
Others came in secretly.
But just ask Jim and John and a guy named Rock in far-away Jerusalem.
Why would the Galatians even care about the specific number of years?
I think the more important division of time and events in this portion of the letter is not generally recognized as a possible solution. I think Paul divided this part of the letter that contains his own back-stories into two broad sections --- what he had already told the Galatians during his visit, and then new events that happened after his visit with them.
Paul’s Galatian readers would readily recognize the division.
First come the parts of his story that he had already told them about before, during his evangelizing visit with them. In the letter, Paul reminded his Galatians about what he had already told them ---
For you have heard of my former manner of life in Judaism, how I used to harass the assembly of God… (Galatians 1:13)
I think Paul continued with his reminder about what he had told them during his visit --- his revelation from God --- his sojourn in Arabia --- and his two-week visit with Cephas in Jerusalem. I suspect Paul probably told a similar back-story to each of his other congregations (the table I posted previously in this thread provides some evidence for that).
I have mentioned before the nature of the letter Galatians as similar to a legal affidavit. Here, Paul makes a transition with new information and events that that he had not previously told the Galatians, including his claim of a second trip to Jerusalem to meet with the three Pillars. An event that Paul used to significant benefit to further his argument against those encouraging his local converts to get circumcised. Paul introduced and “authenticated” that new information with an oath before God ---
Now in what I am writing to you, I assure you before God that I am not lying. (Galatians 1:20).
I think the 14 year interval was included simply to provide an adequate period of time (regardless of the intended starting point) for Paul to have done other things, as well as make a second trip to Jerusalem to meet with the three Pillars, after his visit with the Galatians --- and before the writing of his letter to the Galatians.