Thanks for the post. We see this issue infrequently with Mockups 3 and there seem to be a number of factors which contribute to the issue: the number of wireframes, their relative complexity and the extent of use of certain controls (e.g. the more complex ‘Data Grid’ control).
15Mb - 18Mb is a reasonably large project file but there’s no hard and fast size guide. I have seen projects which are over 50Mb perform fine and smaller, more complex projects which are less than 5Mb have issues.
How many wireframes does your project contain?
To answer your specific questions:
Can Balsamiq mockups be updated without going to a different product?
Unfortunately not - with Adobe Flash/Air coming to its end of life, we’ve had to move on from the Adobe platform as the underlying framework of our desktop app. We’ll continue to support Mockups 3 until January 15th 2021, beyond which the code will no longer be updated.
Is there anything else I can do to help Balsamiq out?
Keeping your project lean and organized is a good habit to be in and it sounds like you’re already there: selecting and deleting unused images; removing unused Symbols; and emptying the Trash regularly will all help.
If you are not super reliant on linking, splitting your project into smaller projects is another way to mitigate performance issues. We tend to think of 100 wireframes as the working limit but, again, I’ve seen much larger projects work fine so it is project dependent.
If you would like us to take a look at your project to see if anything sticks out, we’d be happy to do that - Of course, we’ll only keep it as long as needed for the investigation and only Balsamiq staff will have access.
Just email it to email@example.com. If it’s too large to attach to an email, you can send it via a Dropbox link or using a file-transfer service like https://wetransfer.com/ or such.