So it has appeared in my wallet as we speak. However I'd like to know why it was delayed that long.. Any answer would be greatly appreciated.
The network is busy (it was like that for months now) and your fee (150 satoshi/byte) was not great.
I use to look here for graph on how busy the network is and what's the recommended fee: https://btc.com/stats/unconfirmed-tx
If the mempool is on the rise you should pay more than the recommended fee. And I think that it was on the rise when you've sent the transaction.
Even now it's expected that about half of the transactions that paid 140-160 satoshi / byte take more than 12h to confirm.
