Check the wireless connection in Safe mode with networking (restart the computer and tapping F8 on dell logo. Select Safemode with networking).If the wireless connections is still slow in Safe mode with networking, try updating the update the wireless router's firmware to the latest available.
If the wireless shows the same behavior, update wireless drivers from below link:
If the issue persists, run Network troubleshooter from below link:
For more information, I have provided a link below which can fix the issue:
Below mentioned link would also help you with the settings for wireless internet:
Please reply if you have any further questions.
Thanks & Regards
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