Will the fiber splitter increase or decrease the network speed

Because the passive optical network of the optical fiber splitter uses downlink broadcast and uplink time division multiplexing technology. To put it simply, the server sends the same data to your four optical fibers, and then each of your optical fibers will receive according to your own needs. Your own data, and your data is determined based on time, and transmitted separately. So your delay will be slightly higher than your own use alone (calculated in nanoseconds, can be ignored).
Therefore, to judge comprehensively, if it is not the slowness caused by insufficient website server carrying capacity caused by the excessive number of viewers of the video website, there may be a problem with the optical network construction.