Help, yet to receive a decision mail from the UK visa

[ezechinwa]

Hello guys, I am new to this forum, I applied for a UK visa with my family on the 22nd of May, for a 6 month visit visa for my brother's wedding, this is exactly the 12th working day since we put in our application and we are yet to receive a decision mail from them, although we have only received an acknowledgement mail from Sheffield about the ECO about to make decision. please what can we do, as we might miss the wedding? and why is the process so slow? Is it normal? by the way, we are applying from Nigeria.
Please it is possible that we can still get our passports back on the 15th working day? Thanks