This question is a bit vague - for starters, what is the definition of high traffic?
In cases where I work, we run a combination of manual code from scratch and the areas that are served by the laravel application (this is built into the main site and provides the same amount of traffic as all the old application code).
In areas built using laravel, it has not slowed down (the same database sources are used, and it works on the same web servers, which is useful for testing).
Cautions:
The original manual code is older and does not always use the new PHP methods / design types. This means that it is not as effective as it could be. Then you have overhead when laravel does what you donβt always need / need to continue.
Summarizing
What this means is a layout that you think will be the hardest part of your application in laravel, and then again with custom code. Then compare this shit.
You will most likely find that (good) manual work will be faster. Is it worth the milliseconds? Well, it's up to a personal choice. Laravel is more than capable of handling large amounts of traffic, but of course you could shave a small amount of time without using it.
How important is what you do? If something slows it down and causes problems in Laravel, change it. This is an open source.
For reference (to you, if you consider this as high traffic or not - I would):
This is a UK based SASS that usually caters to visitors from the UK. At 9 pm tonight (Friday evening is actually one of our calmest times), we currently have about 250,000 active PHP sessions running.
The system is serviced through 6 web servers [for redundancy, traffic, etc.] (load balancing) for a PHP application.