Go to the site linked below, put your transaction ID into it (7b115dd0daf41dccbe5dea992c595ad5519d329eb5800510d81e174692034800), and fill out the captcha.
https://www.viabtc.com/tools/txaccelerator/A big mining pool owns the site, and will confirm 100 transactions submitted to it each hour. If the site rejects your transaction then keep trying every hour.
The reason your transaction is delayed is because the network has a high backlog of unconfirmed transactions today, and those with the highest fee get confirmed first.
Each time you send a transaction first check the number of unconfirmed transactions in the network at this site. The site shows there are over 85000 unconfirmed transactions today.
https://blockchain.info/unconfirmed-transactionsIf there's over 10000 unconfirmed transactions you should use a high fee in multibit.
To do that click view, then preferences in its menu as shown below.
The window shown below should open. Move the slider all the way to the right to make multibit classic use a high fee.