For secondary target keywords, should I extend the page or create a new page?

Hi,

I have a page with target keyword X

It ranks well for keyword X, but also for other secondary keywords Y,Z,W...

Let's say I have a short paragraph in the page about keyword Y

Currently I rank on position 8 with the keyword Y. Should I extend that paragraph with more information about Y? Or should I create a separate page with Y as the primary keyword.

Will that kick out the current page from the search results? Will I rank higher, lower or not at all with the new page, since I will not have any backlinks to it?

My current page is already more than 1500 words and I'm worried that users will bounce due to the amount of information.

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thanks,

John