Why does the Power BI Dataset keep on increasing in size ?

We have a Data model connected to two reports with connect live on PBI service.

Currently we are using P2 Gen2.

This Data Model is having Incremental Refresh set up hourly.

The setup for incremental refresh :

number of days archived - 14

Refresh on last 1 day.

The data model is live from past 90 days.

For the first 15 days we monitored the Data model size which used to be around 17-18 GB.

However, currently it has increased upto 26 GB and giving us issues with the refresh.

These are primary checks we have done:

1. We do not see any drastic increase in the data been imported into PowerBI. 

2. We are not calculating any columns during data transformation, it is just connecting to the table and importing the said data. 

3. Some calculations are done inside the model. (measures necessary for the visuals) .

what can be the reason for increase in the data model size? we see 2-3 GB increase every month.

How can we keep this is check? 

We have already done a lot of optimizations in the Data Model, I am not sure how much more we can do (We will still check on this).

The model is already live, so what can be the immediate solution to this issue.

I apologize if we are missing something here. But, any help is appreciated.

Thankyou