What is your weekly distance over last 10 weeks and last year? 20-30km
Age? 32
Training plan - ParkRun once a week, one longer run 10-25km, Running club 1 hour generally speed work/Intervals
Number of runs of 13m or more - 4
Assuming your 10k race was in the last 4-6 weeks and under similar conditions to the half marathon (e.g. temperature, hilliness), I get the following
Greg Maclin Calculator would suggest 1:44 using Very conservative timing. Very Conservative is recommended for average weekly miles under 40mpw, although that is more important for a marathon than a half.
The Fairly conservative (40-50miles per week) time is 1:40:14.
I get about 1:38 from a V̇O2max calculator, which assumes optimal training for the longer distance, which requires much more weekly miles typically.
McMillan puts you at about 1:36:30, but again assumes optimal training for the longer distance.
The warning card for me is when you say you get tired at the end of your long runs, which indicates lack of endurance, which is expected from the low weekly miles. You definitely have the speed to go under 1:40 though.
A lot comes down to risk-reward-fun. If you really wanted to I think you could get under 1:40 but there is a risk by mile 10 you start slowing down a lot. In a half marathon this is not so crucial because you will have less distance o push through. If you have another half coming up soon then I would be conservative for this one and aim for 143 or so, get back to training and increase your weekly miles and then aim for 1:37 or whatever next time.
If you stick to a 1:45 pacer and break away mile 9-10 you should get down to 1:42-1:43 , pass a load of people in the last miles and have a really fun time. If you go out at a 1:35 pace then you probably get the opposite experience but you might just be able to hang on and push through with only a small fade and a lot of gut busting to keep close to that pace, which wont be fun at the time but will be fun looking back.