Santosh,
Do you plan to do MBA by distance or part time or full time on campus?
I'd suggest you to mention the different majors being offered at your b-school.
Further, check up with the alumni as to which specialisation offers better scope.
One could enroll for an MBA for an array of reasons, among which could be,
Decent job upon grduation with high package.
To drift into another field upon doing mba.
Just for a masters degree & be as happy as a king.
Check for the placements and also the majosr that fetch those kind of jobs.
Finally match them with your interests.
In your case, 15 years of hard core experience in chemical sector, you could
easily head the Operations of a chemical company. Major could be Operations.
Secondly, having hands-on experience in accounts, you might specialise in Finance.
Here your competitors at work might be CAs,ICWAs & the like. To get the desired profile in finance you'll have to compete with candidates from top notch institutes.
An MBA in HR fetches both a decent job and more or less a 9 to 6 job.
On major in doing MBA there is lots of speculation - so your interests and the kind of return on investment you expect should be given priority.
goodluck