Training for a race

The photo above will be the running shoes I'll be using for training and eventually for the race.

At the end of the month I'll be running again in a Marathon after 25 years, yes 25 years.The last marathon I run was a 5K during highschool.
Now I will run in a relay marathon were our company has entered a team it will be 16 stages were each stage is 3 km so in short it will be a 3K run for each person. Yah its just 3K but the objective of the is to finish it in 15 min or less if you will do the math you have to run with an average speed of 12 km/hr as for me thats the speed I'm running if I'm doing high intensity run
The last time I timed my run I was able to cover 3K in 17:30.
Right now I'm training for the race so its a mix of endurance run and power run for the next 4 weeks and some core works it means no weight training for the meantime.