Upvote:-2
Sounds normal to me. If you had documents missing first time then they don't need to examine closely, they can just refuse it quickly right away. If everything looks to be in place though then they have to take time to actually examine your documents.
Don't worry about it unless they're a few days beyond what they promised, then you can ask them and they should give you an answer.
I don't think anyone can really give a better answer here unless they work in the relevant office. Who knows what might be going on to cause them to have extra work lately.
Update:
The British Consulate in Chennai for contact details: https://www.gov.uk/government/world/organisations/british-deputy-high-commissioner-chennai
And some data for Chennai's processing times here: https://visa-processingtimes.homeoffice.gov.uk/y/chennai-india/visits-visas/all
99% are done within 15 days though 1% may take up to 30 days.
Upvote:3
The 15 days are just a guideline based on statistics.
As you can see on the Home Office's page for Visa processing times, 99% of applications in July 2016 were processed within 15 days, and 100% within 30 days.
Slightly longer processing times, especially when a previous visa was refused or there are public holidays involved are to be expected.