Sometime in late 2015 the baseballs used by Major League Baseball appear to have changed. How they may have changed and whether it was intentional are hotly contested topics. Regardless of how you feel on the topic, the baseball appears to be traveling five to six feet further now than it did prior to this change.
This flight can be converted to a change in effective velocity, since the ball travels around five additional feet for each additional mile per hour. Meaning the ball has an effective velocity about 1 to 1.2 miles per hour faster than what is registered. Meaning, in order for a ball from the first half of 2015 to fly as far as a ball hit in 2016 or 2017, it would need to have been hit about one mile per hour faster.
You can reverse this logic and say that subtracting a mile per hour from a ball hit in 2016 or 2017 would roughly approximate where it would have landed when using the older baseball. I have run Back in October, after the season had concluded, I ran xStats on a dataset which did just this: it subtracted a mile per hour from the balls hit in 2016 and 2017 and calculated their success rates. You can see the results in the attached spreadsheet.