fix(storage): Increase AsyncWriter default MinLwmValue to avoid frequent flushes (googleapis#15552)

Author: shubham-up-47

google/cloud/storage/internal/async/default_options.cc

@@ -27,7 +27,7 @@ namespace storage_internal {
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN
 namespace {
 
-std::size_t MinLwmValue() { return 256 * 1024; }
+std::size_t MinLwmValue() { return 16 * 1024 * 1024; }
 
 std::size_t MaxLwmValue() {
   if (std::numeric_limits<std::size_t>::digits < 64) {

google/cloud/storage/tests/async_client_integration_test.cc

@@ -451,9 +451,9 @@ TEST_F(AsyncClientIntegrationTest, StartBufferedUploadEmpty) {
 TEST_F(AsyncClientIntegrationTest, StartBufferedUploadMultiple) {
   auto client = AsyncClient(TestOptions());
   auto object_name = MakeRandomObjectName();
-  // Create a small block to send over and over.
-  auto constexpr kBlockSize = 256 * 1024;
-  auto constexpr kBlockCount = 16;
+  // Create a block to send over and over.
+  auto constexpr kBlockSize = 16 * 1024 * 1024;
+  auto constexpr kBlockCount = 3;
   auto const block = MakeRandomData(kBlockSize);
 
   auto w =