Merging similar rows of data, while appending unique data across multiple columns

I have found many similar (but not identical) examples to my issue - but thus far I have not been able to resolve. I am hoping that this post may prompt some guidance.

I am attempting to merge similar (but not identical) rows of data

My source table has 17 columns

Cols 1-14 (A1-N) are often repeated on multiple rows. However where 1-14 match, cols 15-17 (O-Q) are always unique.
There can be one or more versions of these scenarios in the data file (usually no more than 7 occurrences of one matching col-14 series)
My goal is to
* combine the duplicates rows into one for Col 1-14
* append groups of 3 columns to that consolidated row for each unique occurrence of Cols 15-17
* delete the recurring rows (or simply write the consolidated data set to a new sheet)

e.g.

12345678901234AAA
12345678901234BBB
12345678901234CCC
09876543210987DDD
09876543210987EEE

When merged - the output would

12345678901234AAABBBCCC (resulting in a 23 column row)
09876543210987DDDEEE (resulting in a 20 column row)

Any suggestions for accomplishing this would be appreciated.

Thank you