Ykhjuy

I'm flying into Copenhagen from London. I'm arriving at 14:15. I'm looking to book the train from Copenhagen Airport to Linkoping. It leaves at 15:20. Let's assume the plan arrives on time.

Have I allowed enough time for the transfer?

If this is a train that runs more often on the day and your ticket will be valid for other trains on the same day, as common in Denmark for many trains, I would not hesitate to plan on this train, knowing that a late arrival or a delay in getting out of the airport will make me an hour or two late.

On the other hand, if this is a timed ticket, only valid for the train you booked it for, and rather expensive or hard to buy a replacement ticket last minute, I would want to plan for a later train.

A 14:15 arrival from London quite likely means that your plane will have to arrive to London from some other place and that makes delays in departure more likely but in no way sure. Add to that the chance your own flight can be delayed even when the plane comes in on time.

With your time table you may be able to soak up to 30 minutes of delay if you are lucky on everything else. The chances on delays with your flight and within the airport that exceed half an hour are quite high but on the other hand, early arrivals and speedy routes through the immigration and customs process are not unheard of.

It is up to you whether you are willing to take that risk.
(I have not flown to Copenhagen but the times in the answer by @D Manokhin fit with the times I have seen in other EU airports for London to Schengen flights.)

From Trip Advisor:

Under normal circumstances baggage will be on the baggage carousel
maximum 30 minutes after flight arrival.

Customs at Copenhagen Airport is mainly spot checks as you leave the
baggage claim area. There is a green channel for 'nothing to declare'
and a red channel if you have goods to declare.

You will also have to clear immigration (I assume you will be arriving
from outside Schengen area). Immigration is at the end of the pier as
you walk from the plane to the terminal. Waiting time is normally not
more than 5-10 minutes, but can be 15-20 minutes if several
non-Schengen flights are arriving around the same time.

The UK is non-Schengen.

Let's say 30 minutes for baggage (and immigration)

Personally, I think this can be a bit tight, especially if there are a lot of non-Schengen flights. This could be ok if you have been to the airport before but otherwise, you don't know where everything is.

Personally I think it is doable.