Calling Python machine learning service from Java as an OS process or micro service via REST

I am building a web application for business management as a side project and i face an architecture problem. My application will be an Angular web client communicating with a kotlin/java spring back-end via REST. One of the modules of the application will be time series forecasting of sales/orders, and because of the ease of development and the piles of documentation that exists online, i want to build that module in python. That module will generate dynamic html plots that i want to serve to the client. So my question is, it would be better if i do the python part as a stand alone rest micro service with Flask or it's ok to just put the python code inside the java project and call it using ProcessBuilder? Thanks in advance :)