The reindexing operations can take a some time, specially if you have a a significant amount of products on your catalogue. This is because Shopify takes some time to process and send us this data, and therefore, we don't have a way to speed-up this part of the process.
It is highly recommended to rely on real-time indexing to keep your data synchronised with Algolia, and normally triggering a reindex shouldn't be necessary. It is also important to note that when you are running a reindexing operation the real-time indexing is suspended, and therefore, you will experience a delay on updates and data synchronization.